8-BIT CODE LOCK FOR

ELECTRICAL APPLIANCES

FUNCTION:

•This code lock is useful for appliancesrequiring exclusive or authorised useby those who know the preset code.

PRESET 8-BIT CODE

8-BIT COMPARATOR USED TO COMPARE PRESET CODE AND INPUT CODE

INPUT CODE GIVEN BY USER

RELAY CONTROL

ELECTRICALAPPLIANCE

BLOCK DIAGRAM

CIRCUIT DIAGRAM FOR 8-BIT LOCK CODE

1)What is relay switch?

For understanding 8-bit code lock we need to answer following questions?

2) What is comparator?

3) Generally how we give input to IC?

What is relay switch or relay control?

NORMAL OPEN SWITCH

NORMAL CLOSED SWITCH

NC Contact or NO Contact

Spring used to upheld the arm so that it can be in NORMAL CONTACT position

How to change the position of contactfrom NC contact to NO contact??

Controlling 230 AC Volts supply with 5volts DC supply

•What is comparator?

•Digital or Binary Comparators are made up from standard AND, NOR and NOT gates that compare the digital signals present at their input terminals and produce an output depending upon the condition of those inputs.Determines whether the value of input A is greater than, smaller than or equal to the value at input B etc. The digital comparator accomplishes this using several logic gates that operate on the principles of Boolean algebra.

1-bit binary comparator

Inputs Outputs

B A A > B A = B A < B

0 0 0 1 0

0 1 1 0 0

1 0 0 0 1

1 1 0 1 0

TRUTH TABLE:

1-bit binary comparator

Consider two 4-bit binary numbers A and B such that

Here each subscript represents one of the digits in the numbers. For i=1,2,3,4(A=B)

4-bit binary comparator

4-bit binary comparator

4-bit magnitude comparator pin diagram

8-bit magnitude comparator

Generally how we give input to an IC using switch?

Pull-up resistor

 The basic function of a pull-up resistor is to ensure that given no other input, a circuit assumes a default value.

Solution-1 Solution-2

Two-way switch Using pull-up resistors

CIRCUIT DIAGRAM FOR 4-BIT LOCK CODE

4-BIT LOCK CODE FOR ELECTRICAL APPLIANCES